Fig. 7: Schematic representation of the transport mechanism of bAE1.

Coexisting mixed OF–IF a, IF–IF b, and OF–OFc dimers. The relevant TMs (3, 10, and 11) are shown as cylinders. The core domain shifts up and down and rotates in an elevator-like motion with respect to the gate, which uncovers the center of the protein at the cross points of TMs 3 and 10 to either the extracellular or the intracellular solution. The elevator-like motion is combined with α-helical to β-hairpin conformational changes in TM11 and IL5 between TMs 10 and 11. The area of TM11 which unfolds and forms part of the β-hairpin (thick blue and red arrows) of IL5 in the OF state is shown as a red cylinder. The position of H1 with respect to TM11 in the IF and OF states is also included in the figure. The HCO₃⁻ and Cl⁻ ions are shown as cyan triangles and spheres, respectively, and their entry pathways in the protein center in the IF and OF monomers are indicated with black arrows. In the IF state the anions accumulated in the reservoir at the dimeric interface at the intracellular side of the protein move laterally into the IF cavity. In the OF monomers the anions diffuse vertically into the OF cavity directly from the extracellular solution.